The inventive subject matter disclosed herein generally relates to molded articles and methods relating to protective equipment. The molding and manufacturing techniques are particularly suitable for use in the manufacturing of a protective helmet structure for motor sports, including street and off-road motorcycling (including motocross), and human powered or gravity sports, such as bicycling and skiing. In the following description, a motorcycle helmet is used as a representative example of a product of the molding methods according to the inventive subject matter disclosed herein.
Modern motorcycle helmets have two principal protective components: (1) an outer shell made of a thin, hard material and (2) an inner liner of an impact absorbing material. The shell is typically formed of one or more layers of composite or moldable polymer materials based on carbon fiber, fiber glass, aramid fibers (e.g., Kevlar), polycarbonate, and/or acrylonitrile butadiene styrene (ABS) plastic, as well as combinations of the foregoing. The outer shell serves to help prevent penetration of the helmet by a pointed object that might otherwise puncture the skull, to spread the force of impact, and to provide structure to the inner impact liner so it does not disintegrate upon abrasive contact with pavement or objects. The impact liner attenuates impact forces by crushing or compressing. Not only must helmets be safe, but consumers also are looking for lighter weight and better ventilated helmets, among other things.
Conventional helmet shells may be manufactured using a molding process that may be referred to as the “Pressure Bladder” molding technique. The Pressure Bladder molding technique involves layering sheets of a composite onto an inflatable bladder that is the male portion of a male-female mold. The composite sheets may be “prepreg” sheets having an impregnated resin or they may be composite sheets that become treated with a resin in a wet lay-up on the inflatable bladder. The inflatable bladder with the composite sheets is placed into a female mold, and the mold is closed forming a seal. Heat is introduced into the mold to activate the resin, and the bladder is inflated with sufficient pressure to force the composite sheet material into the shape of the mold, which corresponds to the shape of the outer shell.
In the prior art, impact liners have been formed in an injection molding process separate from shells and then pressed into the shells for motorcycle helmets. The pressing process is usually performed by hand and it necessitates that the shell be designed somewhat larger than is ideal so that the liner, which has a larger topside than bottom side, can more easily fit into the cavity of the shell, which also has a small bottom side opening relative to the topside. This relationship in a helmet between the topside and bottom side corresponds to the anatomy of wearer's head and is known as “undercutting”. The larger size increases the weight of the shell. Glue or tape may be used to secure the liner in place. Additionally, it would be more advantageous to structurally fuse the liner with the shell, which should result in a stronger helmet.
Another problem with conventional helmets is that the impact liners, such as EPS foam and similar material are highly thermally insulating, like a Styrofoam cup, which may cause the wearer to suffer discomfort during use. An overheated wearer is not only uncomfortable but may also be impeded from performing optimally during motor sport and athletic competitions. There may even be a risk of dehydration or dangerous lapses of attention resulting from the overheating, especially in certain sports, such as motocross, which may be held in hot climates. Accordingly, a substantial need exists for helmets that do not promote overheating. Unfortunately, dictating against the use of alternative materials to current foams are the substantial advantages that foam has on impact absorption. Foams are also lightweight, which is another factor that is important to wearers and which relates to comfort and performance.
There have been various attempts to improve helmets so that they are less prone to over-heating. Vents have been provided in helmet shells. The vents have an opening in the shell that leads to vent channels formed in the impact liner material, which is typically EPS, or between sections of the liner material. The channels deliver air to the interior area of the helmet, thereby exposing the wearer's head to the air. One of the problems with conventional vents is that the channels must be carefully engineered so that the helmet's ability to absorb impacts is not compromised by the changes in structure. Consequently, there are limitations to how large the channels can be and how they can be routed to deliver air. Another problem is that conventional vent structures formed in a combination of outer shell and impact materials, such as EPS, may result in a gap or rough interface between the opening of the shell and the pressed-in impact liner that is not conducive to good air flow into the helmet, or at least requires extra finishing steps.
In view of the foregoing, there is a substantial need for improved helmets that are stronger and safer, lighter, cooler and more comfortable to use. Some progress has been made at addressing some of the aforementioned problems. See, for example, U.S. Publication Numbers 20050278833 and 20060031978, and U.S. Design Application No. 29/218,313, co-owned with this application, disclose generally a motorcycle helmet and various components. More particularly, a ventilation system is disclosed in co-owned U.S. Ser. No. 11/434,304, filed May 15, 2006; entitled Low Profile Helmet Vents and Venting Systems. These patent applications are hereby incorporated by reference as if set forth herein in their entireties. However, notwithstanding such progress, there is an ever present need for improvements.